8. DATABASE
8.1 DATABASE
Database contains
classes to explore data returned through a content provider or if you need to
manage data in a private database, use the android.database.sqlite classes. These classes
are used to manage the Cursor object returned from a
content provider query. Databases are usually created and opened with
openOrCreateDatabase(String,
int, SQLiteDatabase.CursorFactory).
In our applications we will be mainly
dealing with SQLiteDatabase.It contains the SQLite database management classes
that an application would use to manage its own private database. Applications
use these classes to maange private databases. Exposes methods to manage a
SQLite database.
8.2 SQLiteOpenHelper
To create and
upgrade a database in your Android application you usually subclass
SQLiteOpenHelper . In this class you need to override the methods onCreate() to
create the database and onUpgrade() to upgrade the database in case of changes
in the database schema. Both methods receive an SQLiteDatabase object which
represents the database.
SQLiteOpenHelper
provides the methods getReadableDatabase() and getWriteableDatabase() to get
access to an SQLiteDatabase object which allows database access either in read
or write mode.
For the primary
key of the database tables you should always use the identifier _id as some of
Android functions rely on this standard.
A best
practice is to create per table a separate class which define static onCreate()
and onUpdate() methods. These methods are then called in the corresponding
methods of SQLiteOpenHelper . This way your implementation of SQLiteOpenHelper
will not get to large even if you have several tables.
8.3 SQLiteDatabase
SQLiteDatabase
has methods to create, delete, execute SQL commands, and perform other common
database management tasks.Database names must be unique within an application, not
across all applications.
A simple program is given below here an
edit text is provided followed by a button, on clicking the button the text in
edittext is inserted into database
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package a.b.c;
import android.app.Activity;
import android.database.Cursor;
import
android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import
android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class
DatabaseActivity extends Activity {
EditText e1;
Button b1;
SQLiteDatabase database = null;
String s ;
/** Called when the activity is first created. */
@Override
public void
onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
e1 = (EditText)findViewById(R.id.ed1);
b1 = (Button)findViewById(R.id.bttn1);
database = DatabaseActivity.this.openOrCreateDatabase("Database1", MODE_PRIVATE, null);
database.execSQL("CREATE TABLE IF NOT EXISTS Table1(name
varchar);");
b1.setOnClickListener(new
OnClickListener() {
@Override
public void
onClick(View arg0) {
// TODO Auto-generated method stub
s = e1.getText().toString();
database.execSQL("INSERT INTO Table1 VALUES('"+s+"')");
Toast.makeText(getApplicationContext(),
"Inserted successfully", Toast.LENGTH_SHORT).show();
e1.setText(" ");
}
});
}
}
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main.xml
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
<EditText
android:id="@+id/ed1"
android:layout_width="140dip"
android:layout_height="wrap_content"/>
<Button
android:id="@+id/bttn1"
android:text="Done"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
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Now we will combine list view and
database. The aim of program is to create a database and insert values into it
from edittext on button click on same time list the text from edittext. Also provided
option to delete from database,
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package a.b.c;
import java.util.ArrayList;
import android.app.ListActivity;
import android.content.Intent;
import
android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import
android.view.View.OnClickListener;
import
android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Toast;
public class
Datapass1Activity extends ListActivity {
SQLiteDatabase dbpass = null;
Button b1,b2;
ArrayList<String> list = new
ArrayList<String>();
ArrayAdapter<String> arraydpter;
/** Called when the activity is first created. */
@Override
public void
onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
arraydpter = new
ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,list);
setListAdapter(arraydpter);
dbpass = Datapass1Activity.this.openOrCreateDatabase("Datapass", MODE_PRIVATE, null);
dbpass.execSQL("CREATE TABLE IF NOT EXISTS Tab1(name
varchar(10));");
//ADDING DATA TO LIST
b1=(Button)findViewById(R.id.bttn1);
b1.setOnClickListener(new
OnClickListener() {
public void
onClick(View v) {
Intent
intnt = new Intent(Datapass1Activity.this, second.class);
startActivityForResult(intnt,
0);
}
});
// REMOVING DATA FROM LIST
b2 = (Button)findViewById(R.id.bttn2);
b2.setOnClickListener(new
OnClickListener() {
public void
onClick(View arg0) {
//String s1 = list.get(0).toString();
String s
= list.get(0).toString();
dbpass.execSQL("DELETE FROM Tab1 where name like '"+s+"'
");
list.remove(0);
arraydpter.notifyDataSetChanged();
}
});
}
@Override
protected void
onActivityResult(int requestCode, int resultCode, Intent data)
{
// TODO Auto-generated method
stub
super.onActivityResult(requestCode, resultCode, data);
//HERE NO NEED FOR DCLARING INTENT COZ
INTENT COMES ALONG WITH METHOD onActivityResult i.e, data
Bundle newbun = data.getExtras();
String s = newbun.getString("key");
dbpass.execSQL("INSERT INTO Tab1
VALUES('"+s+"')");
list.add(s);
arraydpter.notifyDataSetChanged();
Toast.makeText(this, s, Toast.LENGTH_SHORT).show();
}
}
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second.java
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package a.b.c;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import
android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class second
extends Activity {
Button b3;
EditText e1;
String s1;
/** Called when the activity is first created. */
@Override
public void
onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main1);
e1 = (EditText)findViewById(R.id.ed1);
b3 =(Button)findViewById(R.id.bttn3);
b3.setOnClickListener(new
OnClickListener() {
public void
onClick(View v) {
s1 = e1.getText().toString();
Intent
intent = new Intent();
Bundle
bun = new Bundle();
bun.putString("key", s1);
intent.putExtras(bun);
setResult(RESULT_OK, intent);
finish();
}
});
}
}
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main.xml
|
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hai"
android:layout_marginTop="20dip"
android:layout_gravity="center_horizontal"
/>
<TextView
android:id="@+id/tv1"
android:text="What do you
want to do...?"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="40dip"
android:layout_gravity="center_horizontal"/>
<Button
android:id="@+id/bttn1"
android:text=" Add to list
"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:layout_gravity="center_horizontal"
/>
<Button
android:id="@+id/bttn2"
android:text=" Remove from
list "
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:layout_gravity="center_horizontal"
android:onClick="remove"/>
<ListView
android:id="@android:id/list"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</ListView>
</LinearLayout>
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main1.xml
|
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<EditText
android:id="@+id/ed1"
android:layout_width="150dip"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dip"/>
<Button
android:id="@+id/bttn3"
android:text="Click to
enter to list"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:layout_gravity="center_horizontal"/>
</LinearLayout>
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While using additional activities don’t
forget to add them in manifest. Also provide an xml for each activity.
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